The present invention relates to a method for thermally printing a pre-selected dye image onto a three dimensional object using flexible heating elements. Particularly, the heating elements are carried by a dye image carrier sheet or membrane which conforms tightly to the shape of the object during the printing operation.
The dye image carrier sheet and membrane, which carry flexible heating elements in accordance with this invention, can be used with the thermal-transfer printing system described in published United States Patent Application US 2002/0131062 to Neri and Mutter (“'062 Publication”), the disclosure of which is hereby incorporated by reference.
In general, the printing system described in the '062 Publication involves placing an image carrier sheet containing a pre-selected, dye image over a three-dimensional object and thermally-transferring the image to the object. An example of a suitable three-dimensional object is a plastic cover for a cellular telephone or a computer mouse. The three-dimensional object is placed on a bed assembly, and the image carrier sheet is laid over the object. A flexible membrane is drawn over the image carrier sheet by a vacuum. As the vacuum draws the membrane and image carrier sheet into pressurized contact with each other, the carrier sheet is wrapped around the various surfaces of the object. The image carrier sheet and object are maintained in pressurized engagement with each other by the vacuum. Then, the printed dye image on the carrier sheet is transferred to the object by heat. In the '062 Publication, a heating assembly containing multiple tubular heating lamps is located above the bed assembly containing the object. The heating lamps are energized so as to heat the image carrier sheet and thermally-transfer the dye image to the object.
Durand, U.S. Pat. No. 4,670,084 discloses an apparatus, wherein dyes are thermally-transferred from image sheets to objects such as computer keyboards. A flexible membrane is drawn over the image sheet and the image is transferred to the object by heat and pressure. The apparatus includes a hood containing multiple heating lamps and parabolic reflectors which reflect heat radiation from the lamps downwardly onto the object. One drawback with the heating assembly described in the Durand, '084 Patent is that the mounted heat lamps are shown being located at some distance from the image sheet and object that will be printed thereon. The heating lamps may not emit heat radiation uniformly to each area of the sheet and object. As a result, the printed image, which is produced on the object, may be of poor quality.
Denley, U.S. Pat. No. 4,792,376 discloses a different thermal-transfer printing system for printing legends on the keycaps of keyboards. The system includes an air-inflatable heated bladder that applies heat and pressure to a legend-carrying medium such as a paper. According to the '376 patent, the keycaps first must be moved from a keyboard profile to a planar printing profile before the legends are printed on the keycaps. The air-inflatable bladder contains chambers which hold electrically-heated quartz rods. This thermal-transfer printing system also has several drawbacks. Particularly, the legends are only printed on the top surfaces of the keycaps. The keycaps must be arranged in a planar position in order to receive the legends. Also, the heated bladder is not drawn completely over the keycaps. Rather, a printing platen is moved down upon a printing fixture which supports the keycaps and paper medium.
In view of some of the disadvantages with some conventional thermal transfer-printing systems used to print dye images onto three-dimensional objects, there is a need for an improved method. The present invention provides an improved method. In the method of this invention, flexible heating elements are used to thermally-transfer the image onto the object. The flexible heating elements are carried by a dye image carrier sheet or membrane that enwraps the object, or by both the image carrier sheet and membrane. When energized, the heating elements apply heat uniformly to the image carrier sheet and the dye image is transferred to the object completely and cleanly. The printed image, which is produced on the object, has good print resolution, brightness, and overall quality. These and other objects, features, and advantages of this invention are evident from the following description and illustrated embodiments.